Fused, polarized, blade-type electrical coupling



C. R. CURTIS June 30, 1953 FUSED, POLARIZED, BLADE-TYPE ELECTRICAL COUPLING Filed April 29, 1950 INVENTOR. g faence JE. "afjzs Patented June 30, 1953 FUSED, POLARIZED, BLADE-TYPE ELECTRICAL COUPLING Clarence R. Curtis, Lombard, Ill., assignor to F. H. Smith Manufacturing Company, Chicago,.Ill., a corporation of Illinois Application April 29, 1950, SerialNo. 159,037

This invention relates to a fused, polarized, blade-type electrical coupling. The specific coupling shown is a' male to female blade-type adapter. It is one of several inventions relating to small electrical couplings such as those that are used to make connections .between lamps and household appliances and domestic branch lines. These inventions have common features resulting from certain overlapping objectives. In this application, the entire development will be generally described sothat the other applications may be short and directed to a specific improvement.

In order to avoid confusion in terminology, the terms used in the Standard For Attachment Plugs and Receptacles published by Underwriters Laboratories, Inc., will be followed. Applicants devices are concerned primarily with electrical couplings employing polarized blades and usually polarized female contacts to receive such blades and not with couplings employing either male or female threaded members, but it is true that some of applicants features could be adapted to threaded type couplings. An attachment cap is an insulated housing in which is joined a pair of wire conductors to a pair of blades, and may be contrasted with an attachment plug in which is joined a pair of wire conductors and` a male threaded shell. A cord connecter is an insulated housing in which is conductively joined a pair of wire conductors to either a threaded female socket or a pair of female contacts for blades, but as used herein means only the latter. A "receptacle is an insulated housing having either a threaded socket or a pair oi slots behind which are female contacts to receive blades, but as used herein means only `the latter. A tap is an insulated housing in which is conductively joined a, pair of branch line wire conductors to one or more receptacles. An adapter is an insulated housing in which 11 Claims. (Cl. 20o-115.5)

line housing through which passes two conductors insulated fromv each other and each terminating in a blade. Apart from Underwriters Laboratories terms, the term cord includes appliance cords and lamp cords. The ordinary lamp cord is 16- to l-gauge stranded wire. Some appliance cords are about the same weight, but others such as those for toasters, refrigerators and electric irons are heavy, as heavy as the branch line l-gauge solid conductor. These cords, however, are also stranded.

The single fused polarized adapter herein disc closed was designed to reduce the fire hazard a pair of blades is conductively joined to one or more pairs of female contacts. A polarized atta-ehn'ient cap is one in which the .ground a generic term to describe any small, branch resulting from frayed strands of lamp and appliance cords, and not as an auxiliary protection to a branch line fuse or to save a householder the trouble of replacing a burned out branch line fuse. To appreciate the safety features, one must understand the effect of forty years of successful pressure by the power cornpanies and appliance manufacturers against the fire underwriters to increase the branch line fuse load while the wire weight in the branch lines remained constant. Prior to 1913, the underwriters had approved a 6-ampere fuse for -a branch line. On this current amplitude was predicated the size wire to be used in branch lines, orvice versa. A lLi-gauge solidwire will safely handle S-amperes, and this was the UnderwritersV Laboratories approved gauge. This weight wire is commonly used and has been used for several decades, in building, particularly in walls. gauge is commonly 16- and 18-gauge, but importantly, the wire is not solid but stranded, and in the starting of res, this is important, as will be explained later.

During the past fifty years, the number of branch lines in a given dwelling or building has usuallyr remained unchanged., and the power companies would have been limited to selling a -ampere load on each branch line so long as only a B-ampere fuse could be used. The power companies have steadily pressed the underwriters to raise the load limit, and in 1913, the underwriters raised the fuse limit to ten amperes. In 1922, the present standard fuse `of fifteen amperes was approved. In some localities, the underwriters have approved for an appliance line only a 2li-ampere fuse for a 12-gauge solid wire ine.

It is apparent, therefore, that even a l5- ampere fuse may not protect 16- and l8gauge stranded cord wires attached to a branch line. Applicant has made tests which show that where For appliance cords, howevenfthe a l-ampere fuse circuit positioned within onefourth inch of cotton batten is shorted, the cotton batten will burn.

This danger admittedly, however, is not great because branch lines are lying in walls, frequently in metal tubing or BX casing, where insulation wear is unlikely. In the case of appliances and light cords, however, these are exposed to many kinds of wear and would become dangerous even if they were solid wire conductors. In fact, they are stranded, and applicants tests show that where the strands are .O10 inch diameter, and a strand is broken from the wire and grounded close to inflammable material, an 8-ampere fuse constitutes a borderline protection, because sometimes the wire burns and starts a re while other times the fuse burns. Any larger fuse will result in the wire burning. Light cord wires are commonly composed of strands having .006 inch diameter. For this size strand, under the same conditions, a 5-ampere fuse constitutes borderline protection.

Applicant conducted many experiments and reached the general conclusion that it is possible to set upconditions where a fuse no matter how small, would not be protection against fire. As a practical matter, wlhere the strands of an appliance cord have a gauge of .O06 inch, a 3- ampere fuse is positive protection against a positive short. IOn strands of a gauge of .010 inch, a 6- or 8-ampere fuse is positive protection aaginst a positive short. These conclusions are good irrespective of how one separates the strands or how one grounds them,

It happens that most lamp and somo appliances do not draw more than three amperes and it follows that such a fuse will adequately protect the cords of such appliances.

The foregoing conclusions may be affected by the length of the extension cord. It is recognized that whether or not a l-ampere fuse will burn depends in part on the length of the branch line and the length of the extension cord in which the short occurs. The longer each. is, the more resistance and impedance there is in the line, and the more strands of each wire must short circuit in order to blow the fuse. By the use of applicants adapter with its smaller fuse, only the extension cord is a factor. They will work on any reasonable length depending upon the size fuse used. This is. exceedingly desirable. The chief electrical inspector for the city of Chicago is recommending for the new City Code a branch line limit of 40 feet and a lamp cord limit of 6 feet, of course, predicated only upon the existence of a single branch line fuse. This would seriously limit the use of lamps.

The nrst object of this invention is to protect attachment cords from hashing that would create a nre. The protection afforded may incidentally protect an appliance or a branch line fuse, but the primary object is to avoid the dangers which flow from a frayed, stranded wire cord.

The problem of protecting an appliance cord i is this. A fuse may be placed in the hot line of a cord attachment cap, or in the ground line, or a fuse may be placed in each line. Of these three possibilities, the fuse in the hot line is the best. If the fuse is in the ground line, and it burns, the hot line in the cord to the appliance is still at branch line potential and the short may find a new ground. If the fuse is in the hot line and it burns, all of the wires in the cord and the appliance are at ground potential and safe. Manufacturers of some fused attachment plugs have sought to solve this problem by placing two fuses in an attachment plug, one in each line, but the fuse in the hot line will not necessarily blow where there is a fuse in the ground line. On the other hand, a fuse in only one line of an unpolarized electrical coupling may, when assembled, be in the ground line, leaving the lhot line at full potential even after it has blown.

Either of these last two solutions protect the branch line fuse and therefore act as a convenience to the householder. Neither accomplishes applicants object of safety, because by either, an appliance line may remain hot and a strand at branch line potential may nd a new ground, and start a lire.

rDhe feature of al1 of applicants couplings is the provision of a coupling having either polarized blades or polarized slots with a replaceable fuse in the hot line onlyy with instructions that the fuse to be used is based on the fusing point of a wire strand and not of an entire wire.

The second object of this invention is to provide a cartridge fuse chamber which so holds a cartridge fuse that neither the chamber contacts nor the fuse contacts are accessible when the coupling is energized. Applicants couplings have been designed around the 1% by 1A inch cylindrical cartridge fuse which is widely available in many amperage ratings and in both the regular and delayed action types. Some of the problems encountered stem from the use of this cartridge fuse, problems that might be avoided by an especially designed fuse. These problems are outweighed by the ready availability of these fuses.

It is important that the householder not disassemble a coupling housing in order to replace a fuse, which means that the fusev must be placed in the housing through an opening. If this opening is through the surface from which the blades extend, the surface will be closed when the blades are mounted in a receptacle. The cartridge fuse must be positively held in the line in order to transmit current while keeping the temperature at a desired minimum. Underwriters Laboratories has no requirements as to the pressure that must be exerted by fuse holders upon the fuse electrodes. Applicants experiments show that a one-pound pressure exerted against the ends of a fuse will sulce, and in order to be fully protected, his contacts actually exert a three-pound pressure. It follows that a fuse cannot be merely dropped into position between electrodes. It must be forced. Conceivably, if the fuse cartridge is to -be removed, one must either have a means for pulling it out through the fuse chamber opening or must be able to get at the cartridge from some other side of the housing and push it out. Others have provided such openings and invariably an end electrode of a fuse or a xed contact within the coupling could be contacted by a knife or wire from` some side of the housing other than the blade side.

The cartridge fuses consist of two metallic end caps or electrodes spaced from each other by a tube made of insulating material such `as glass, plastic or ceramic, and a feature of applicants invention resides in positioning an opening called a fuse ejector aperture in the housing wall which will permit access only to the insulated (glass) portion of the cartridge with the result that a c'hild can probe with a wire around one of applicants adapters positioned in a wall receptacle and not make van electrical contact. y

Another object -of this invention is to utilize the fuse-holding means as a fuse ejector. `Applicants cartridges are vheld by end-engaging electrodes, one of which is iixed, 4and 'the other of which is flexible, and the walls of the .fuse chamber leading into the exterior opening rare so related to the nal position of the cartridge that the cartridge is snapped into contacting position Kand by means of the flexible electrode and ejector aperture maybe snapped out of the chamber.

Another object of this invention. is to provide Ia heavy gauge spring contact that will not take a set with the passage of time. Underwriters require that female contacts hold a pair of blades against a pull of three pounds. This creates a problem of tensioning copper conductors against each other `and usually this is done by providing a fulcrum or bending point from which the pressure conductor functions. Applivcant does two things which arev beneficial. He

places his fulcrum point .at a Asubstantial distance from the actual contact point of the .conductor and thereby extends its bending over ya substantial length of metal, with the result that his contact may be under tension holding a fuse cartridge lor a blade without losing its elasticity. Secondly, he places the axis `or the fulcrum of an electrode used -for a blade parallel to the movement of the blade into its socket.

The foregoing objects are Aapplicable to :applicants adapters, attachment caps, and wall receptacles, one of which is shown in this applica- 7' tion, but all -of which may be equipped with fuse receptacles. The present .application relates specifically to an adapter and .applicant provides a lock screw for converting this adapter into an attachment cap. that are dangerous are those which are connected to the appliance whether 'it is being used or not. Thus, lamp, refrigerator, radio, television and clock cords are continuously lconnected. If fire develops when people are around, it ordinarily is detected and extinguished. The trouble usually arises lwhere the cord passes under a rug or curtain, or .near a mattress. andfis .abraded 'or frayed by use. Finally, the frayed section `:allows critical :shorting of at least part of the strands. It may :be half an hour or so before .spitting hot copper causes a smoldering rug .to name. 'The ideal would be to replace the attachment cap, -but this involves removing the existing attachment cap which, in turn, requires some mechanical skill, and in the case of the rubber molded plugs, cannot be done. Applicant, therefore, 'is providing an adapter which may be .positioned inv termediate the attachment cap Yand the wall receptacle. Moreover, it would be beneficial if the connecter could be semi-permanently attached vto the cap.

A speciiic object of the present invention is to provide means :for-quickly ylocking applicants 1adapter to the blade of an attachment cap.

Referring now to the drawings:

Fig. l is a perspective View rof the blade V'ia-ce of an adapter;

Fig. l2 is a perspective View of the receptacle face of Yan adapter;

Fig. 3 is an Aexploded perspective Yview of `the 'elements oi' the adapter;

Fig. 4 is a planview of the inside 'of v.the adapter base with the elements mountedtherein;

In a house, the cords L Fig. V5 vis a view taken on theline 5-5 of .1.;

Fig-6 is a plan view of the ejector windowzside of the adapterand partly cut away; and,

Fig. 'I vis a view taken on vthe line 'I- of Eig. 16.

Continuing to refer to the drawings, the numeral I0 identiiies a base Vpanel formed of a phenol compound or other suitable insulating material. Formed integrally with this panel on' one side thereof is a land [2. A pair of through slots, Irl Yis small for a hot line blade, and -IG is larger for a ground blade, penetrate the panel and the land, see also Fig. 5. Along one inside `edge of the panel iii is a Wale I8, which forms lwith the adjacent side of the land l2 a concave fuse seat 22 into which may be rested a cartridge fuse 2li. The cartridge fuse is composed of two metallic caps 25 and 21 spaced 'by a glass or other insulating material tube 29.

Through one side of the land I2 is `a Vpassageway 2B and seated in this passageway is a heavy, elastic, conductive, metallic, 'IJ-shaped .strap 28. Referring to Fig. 4, the strap -28 follows the curvature of the land I2 so that its end 36, acting as an elastic Contact, is movable axially of the fuse seat 22, and thereby constitutes a fuse holder. The central portion 38 of the strap 28 is held adjacent to the land by the side wall '32, see Fig. '7, of a cap member 3K1.

Returning to Fig. 4, the strap 28 bends from the point 38 as far as the contact 36, the bending lat any point being comparatively small. rihis small amount of bending at any given point in the arm di! makes it possible to use a heavy gauge Vmetal for the strap 23 which in turn places the necessary tension on the fuse .214 so as to hold it firmly in position. The arm i2 is also long and pla-ces the necessary tension on a blade entering the opening i4. Returning to Fig. 3, there is an outwardly turned tongue 44 on the arm 42 which is rst engaged by an entering blade 'and which blade cams the arm 42 outwardly and establishes a rm Contact with it.

Referring to Fig. `3, a flexible spring 4t is seatable in the opening 4S of the land I2. As viewed -in Fig. 4, this spring vhas a reverse question mark vconiiguration with the inner end 5t flared outwardly so that a blade entering at opening will be cammed inwardly of the opening 52 .in the strap 46.

Adjacent the wall 54 of this strap is seated a yblade 5B having a Wale 58 across its base. This blades left-hand surface and wale 5B are aci-- jacent the opening I6 vso that when a blade from an attachment cap is inserted, the portion 50 Wil-1 press it against the blade 56 and a good connection will be established from the incoming vblade directly to the blade 56.

The -hot line blade is indicated by the numeral and is joined to a contact or fuse holder 62 by an 'offset portion S. The side shape. of this blade is indicated in Fig. 6. Figure #i shows a vfuse 24 positioned between the contacts and 36.

.Referring to Fig. 3, the cap 'M has slots t@ and 68 to pass the blades E@ and 5S respectively. The cap 34 carries a hole TIE) in. which may seat a locking screw 'I2 which passes through a hole 'ber TI.

M in the base I0..

Returning to the cap td, there is an opening 'It .in its front wall through which may be inl serted a fuse cartridge into the cartridge cham- The opening is indicated in greater dereverses its direction at B2, leading to the iixed position contact 62. In order to insert a fuse, one end is introduced through the opening I6 as indicated by the dotted outline of the fuse 84. The contact 36 is in the position indicated by the dotted line 86. When the fuse reaches the position indicated by the dotted line 83, a screw driver or pencil or knife 90 is pressed against the end of the fuse, which retracts the contact 36 into the solid line position indicated by the numeral 36v and the fuse seats against the fixed contact 62.

Figure 6 also shows the ejector window, bearing the numerals I0!) and WZ, the window being formed principally in the cap il@ but partly in the base I0. The ejector window |00 is in vertical. alignment, as viewed in Fig. 6, with the opening 16. Referring to Fig. 3, the portion |02 of the window penetrates the fuse seat 2E. In order to remove a fuse, a knife |04, referring to Fig. 7, s

passing through the window |953 cams the fuse 24 outwardly along the surfaces 82 and 8B, see Fig. 6, and when the fuse reaches the position Bil in Fig. 6, the spring contact 35 forces it along the surface 80, thereby positively ejecting the fuse from the housing.

This connector possesses another feature, namely, the lock screw Ili. This lock screw, see Fig. 3, has a screw driver or other standard recessed slot |08, and it rides in a guideway IIiI, see Fig. 5, which is adjacent to the through hole I6, see also Fig. 2. The screw |06 rides freely in the guideway IIO, and its screw driver slot |08 is accessible through a hole IIR in the cap, but having a diameter such that the screw |06 cannot drop out. When a blade IM is inserted through the opening I6, referring to Fig. 5, the screw is pushed out of the way until the blade reaches the position indicated by the arrow I|5 in this figure. Thereupon, a small screw driver is passed through the opening I I2 and the screw is turned down, cutting its way into the blade I I4 and holding it tightly against the guideway ||0. There are no threads in the guideway IIO. Screw |06 engages a ground blade.

The advantage of this screw |06 is to make it possible to quickly convert an ordinary attachment cap semi-permanently into a fused attachment cap. A householder who wishes to protect a radio or light cord already installed, could cut off the existing attachment cap and substitute therefor a fused attachment cap, not shown in this disclosure. This, however', involves cutting cords and other work. Moreover, the removed attachment cap particularly if it is a rubber one, will be thrown away. This is entirely unnecessary in the case of applicants adaptor. The user can simply mount the adaptor on the end of the attachment cap and then can turn down the lock screw |06 semi-permanently aixing the adaptor to the attachment cap. The adaptor cannot be inadvertently removed as when a vacuum cleaner or radio cap is withdrawn from a wall receptacle. It, of course, can be removed by a tool that will loosen screw IIlB.

For factory use, applicant will provide a polarized fused blade-type attachment cap, but for existing attachment caps he provides this adaptor which can be used either to protect a particular lamp or appliance by locking it to its attachment cap, or it may be used on given wall outlets where the attachment caps will be changed from time to time. In which latter case, the screw |06 is not tightened..

An important factor contributing to the success of this adaptor is the flexible end contact 36, see Fig. 6, and to a lesser extent the fixed end contact 62. As heretofore explained, applicant requires a three-pound push to mount or remove a fuse from its holding electrodes. If applicant substituted clasps to grasp the cylindrical sides of the fuse with their openings toward the receptacle opening 16, the knife applied through the ejector opening |00 would clear the righthand end of the fuse, but would not clear the other end. There would be some diiculty in getting the fuse out of the small opening 16. Assuming that a clasp was substituted for the xed electrode 62 and the exible end contact 36 retained, the ejecting feature of applicants invention would be retained. It would also be possible to cut back the wall 18 in Fig. 6 similarly to the wall 30 so that the opening I6 was much wider and then push clasps to hold the fuse. If the ejector aperture |00 was centered on the fused cartridge, ejection by means of a knife would probably work, at least after a fashion. Here, however, the recess 'I6 would be undesirably wide, and mounting the fuse in the clasps would be denitely more difficult than is the present mounting of simply pushing back the contact 36 as the other end of the fuse is pushed down the inclined wall 82.

By placing a fuse only in the hot line, of an appliance cord, the danger of iiashing due to snorted strands is very nearly eliminated because a 16- or 15S-gauge strand when shorted will burn any fuse up to three-amperes and a threeampere fuse is sufficient to handle most household equipment. It will handle a 300 Watt lamp. There lare `some circuits that require a greater amplitude, i. e., 500 watt lamps or electric motors for refrigerators. In these cases, a heavier fuse must be used, but even here the fuse is not likely to be over 5- or -ampcres which is proportionately more protective than the 15ampere branch line fuse.

Having thus described the invention, what is claimed is:

1. A fused, polarized, electrical coupling comprising an insulated housing, a pair of through conductors insulated from each other therein, one terminating in a ground blade and the other in a hot line blade having a smaller cross section than the ground blade, and a removable cartridge fuse in the hot line.

2. A fused, polarized, electrical coupling comprising an insulated housing, a through conductor terminating at one end in a ground blade, an electrode within the housing, a hot line blade having a smaller cross section than the ground blade and connected to an electrode within the housing, a second electrode spaced from the first, one of said electrodes being made of spring metal and movable toward the other, and a cartridge fuse removably held by its ends between the two electrodes.

3. A polarized, blade type electrical coupling for carrying a removable fuse comprising an insulated housing, a flat external surface on the housing, a through conductor terminating at one end in a ground blade projecting through said surface, a fuse chamber within the housing, there being an opening through said surface into the chamber, spaced electrodes in said chamber, means for connecting an outside conductor to one of said electrodes, a hot line blade having a smaller cross section than the ground blade and connected to the other electrode.

4. A polarized, blade-type electrical coupling for carrying a removable fuse comprising an insulated housing, a nat external surface on the housing, a through conductor terminating at one end in a ground blade projecting through said surface, an elongated fuse chamber within the housing adjacent said surface with its length substantially parallel thereto, there being an opening through the Wall of said surface into the chamber, spaced electrodes in said chamber, one of said electrodes being made of spring metal and movable toward the other, and a hot line blade having a smaller cross section than that of the ground blade connected to one of the electrodes.

5. A polarized, blade-type electrical coupling for carrying a removable fuse comprising an insulated housing, a flat external surface on said housing, a through conductor terminating at one end in a ground blade projecting through said surface, an elongated fuse chamber Within said housing and having its length substantially parallel to said surface, a flat electrode at each end of said chamber with their fiat surfaces generally facing each other, there being an opening through the housing Wall into the chamber adjacent one of the electrodes, the other electrode being made of spring metal and movable toward the other, and a hot line blade having a smaller cross section than the ground blade connected to one of the electrodes.

6. A polarized, blade-type, electrical coupling comprising an insulated housing, a flat external surface on said housing, a ground blade and hot line blade having a smaller cross section extending from said surface, a through conductor terminating in the ground blade, an elongated fuse chamber in said housing and having its length substantially parallel to said surface, an opening through the said surface of sufficient size to pass a cartridge fuse into said chamber, a flat electrode at each end of said chamber with their flat surfaces generally facing each other, one of said electrodes being made of spring metal and movable toward the other, and a conductor connecting the hot line blade to one of the electrodes,

7. For use with a standard cartridge fuse having two end electrodes spaced by an insulated portion, an electrical coupling comprising an insulated housing, a ground blade and hot line blade of smaller cross section extending from one surface thereof, a through conductor terminating in the ground blade, a fuse chamber within said housing, there being an opening in the blade face of the coupling into the fuse chamber through Which may be passed a cartridge fuse, spaced electrodes in said chamber adapted to engage the fuse electrodes, a conductor connecting the hot line blade to one of said electrodes, and an ejector Window into the chamber through a housing Wall other than the blade face of the coupling into that portion of the chamber occupied by the insulated portion of the fuse.

8. A polarized, blade-type, electrical coupling comprising an insulated housing, a ground blade and hot line blade of smaller cross section extending from one surface thereof, a through conductor terminating in the ground blade, a fuse chamber in said housing, an opening through the outside wall of the housing of suiiicient size to pass a cartridge fuse into said chamber, spaced electrodes in said chamber, a pair of electrodes in said chamber adapted to engage respectivelythe fuse contacts, a conductor connecting the hot line blade to one of said electrodes, an opening in the blade face of the housing into the chamber adjacent one of the electrodes, theother electrode being made of spring metal and movable toward both the first electrode and diagonally toward said opening, and an ejector window through a housing wall other than that of the blade face of the housing and into that portion of the fuse chamber only which is occupied by the insulated portion of the fuse.

9. A male to female, fused, electrical adaptor comprising a housing, a ground blade and a hot line blade of smaller cross section extending from one side thereof, a through conductor connecting the ground blade to a female contact, a fuse chamber within said housing, there being an opening through the housing wall into said chamber, a pair of spaced electrodes in said chamber, a conductor connecting the hot line blade to one chamber electrode, and a conductor connecting the other electrode to a female contact.

10. A polarized, blade-type electrical coupling for carrying a removable fuse comprising an insulated housing, a through conductor terminating at one end in a ground blade, a fuse chamber, a fixed electrode in said chamber, a smaller hot line blade connected to said electrode, a secondelectrode in said fuse chamber and springloaded for movement toward the iirst, there being an opening in the blade Wall of the coupling into said chamber, and a Wall sloping away from the xed electrode toward the opening, whereby when a cartridge fuse has one end cleared from the fixed electrode, the spring-loaded electrode will eject it down the sloping wall and out the opemng.

ll. A polarized, blade-type, electrical coupling for carrying a removable fuse comprising an insulated housing having a at external surface, a through conductor terminating at one end in a ground blade projecting through said surface, an elongated fuse chamber within the housing having its length substantially parallel to said surface, there being an opening through said surface through which a glass-type cylindrical fuse may be passed into the fuse chamber, a fixed electrode at one end of said chamber, a'flat electrode at the other end of the chamber, said latter electrode being made of spring metal and movable toward the first electrode, a 'Lhot line blade having a cross section smaller than that of the ground blade connected to one of the electrodes and projecting through said surface, and an ejection Window through a Wall of the housing adjacent the flat surface into the fuse chamber between the electrodes.

CLARENCE R. CURTIS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,180,648 Hubbell Apr. 25, 1916 1,731,039 Belden Oct. 8, 1929 1,942,178 Machenheimer Jan. 2, 1934 1,974,700 Adams Sept. 25, 1934 1,990,176 Fried Feb. 5, 1935 2,176,793 Fry Oct. 17, 1939 2,201,427 Carr May 21, 1940 2,289,172 Beal July 7, 1942 2,496,413 Sciara Feb. 7, 1950 FOREIGN PATENTS Number Country Date 674,960 France Oct. 28, 1929 

